Are both of the following proper English or only the second one?
1: You are very bad work manager.
2: You are a very bad work manager.
No. Only the second sentence is grammatically correct. That's because all countable nouns (nouns representing things that can be counted as opposed to nouns representing things that normally can't be counted like money, knowledge, anger and many others) in English require the use of an indefinite article that's placed in front the noun or other descriptive words such as adjectives that might already be in front of it.
English has only two indefinite articles: a and an. They're absolutely identical in their function. The only difference is that a should precede words that begin with consonants (letters like b, c, d etc.) and an is used with words that begin with vowels (a, e, i, o etc.).
So, a noun like programmer is a countable noun because programmers are things that can be counted numerically. This means that with the word programmer we should be using the indefinite article a:
You are a very good programmer.
A noun like money is uncountable because in English it represents something that cannot be counted. In other words, you can't say a money or moneys. Saying something like that sounds patently wrong. So, there should be no article in front of it:
As a programmer, I'm making pretty good money.
Although article usage in English is a lot more complicated than what I have described here, my explanation should be enough to help you get the gist of it.